1. Field of the Invention
The present invention relates to a substrate for an electro-optical apparatus, an electro-optical apparatus, a method for driving the electro-optical apparatus, an electronic device, and a projection display apparatus.
2. Description of the Related Art
Semiconductor technologies for forming single-crystal silicon thin films on supporting substrates and forming semiconductor devices on the silicon thin films are called silicon-on-insulator (SOI) technologies, and have been widely studied since they have advantages, such as high-speed response of transistor elements formed of the silicon thin films, low consumption of electrical power, and high integration.
In general, growth of polycrystalline silicon on insulating layers is easy whereas growth of single-crystal silicon is difficult. Use of SOI technologies, such as separation-by-implanted oxygen (SIMOX) methods and adhering methods, therefor, has been studied. In the SIMOX method, oxygen ions are implanted into a single-crystal silicon substrate to form an insulating layer composed of a silicon oxide film in the interior of the single-crystal silicon substrate while leaving the single-crystal silicon layer at the surface. In the adhering method, thermal oxide films are formed on the one surface or the two surfaces of two single-crystal substrates, these substrates are adhered to each other, and then one of the single-crystal substrates is thinned by shaving to form a device layer. In a disclosed application of the adhering method, hydrogen ions are implanted into a single-crystal silicon substrate, this substrate is adhered to a supporting substrate, and then the thin film silicon layer is separated from the hydrogen-doped region of the single-crystal silicon substrate by thermal treatment (U.S. Pat. No. 5,374,564). In another disclosed application, a single-crystal silicon layer is epitaxially deposited onto a silicon substrate with a porous surface, the silicon substrate is adhered to a supporting substrate and detached, and then the porous silicon layer is etched to form an epitaxial single-crystal silicon thin film on the supporting substrate (Japanese Laid-Open Application No. 4-346418).
MOS semiconductor devices having such a thin film SOI structure have parasitic capacitance smaller than that of general bulk-type MOS semiconductor devices. Problems in bulk-type MOS semiconductor devices, that is, junction capacitance between source/drain regions and a substrate and wiring capacitance formed between the substrate and wirings formed on the substrate, are significantly moderated in the MOS semiconductor device having the SOI structure as compared with the bulk-type MOS semiconductor devices, since at least the surface of the substrate is composed of an insulating material. Furthermore, the MOS semiconductor device having the thin film SOI structure does not form a current path in a deep layer at the substrate side which is problematic in the bulk-type MOS semiconductor device, and thus is resistive to a so-called punch-through phenomenon.
Substrates provided with such a MOS semiconductor device having the SOI structure (SOI substrates), as well as substrates provided with conventional bulk-type MOS semiconductor devices (bulk-type semiconductor substrates) have been used in production of various devices, and have an advantage, that is, possible use of various materials as supporting substrates, unlike the conventional bulk-type semiconductor devices. Usable supporting substrates include transparent quartz glass and general glass substrates in addition to general single-crystal silicon substrates. As a result, for example, formation of a single-crystal silicon thin film on a transparent substrate enables formation of high-performance transistors in optically transmittable devices, for example, a transmissive liquid crystal display device using single-crystal silicon having high crystallinity.
Although the MOS semiconductor device having the thin film SOI structure has many advantages as described above, it has a problem, that is, a substrate floating effect. The substrate floating effect means accumulation of excessive carriers in channel regions without emission because of the insulating substrate surface provided with substrate transistors. When the channel in a thin film transistor having SOI structures is composed of single-crystal silicon layers having high electron transportability, potential difference generated between a source and a drain will readily result in accumulation of carriers (charges) in the channel regardless of an OFF state of the thin film transistor. When the transistor is in an ON state, an excessive current will readily form. When such carriers (charges) are accumulated or flow in the channel of the thin film transistor, the excessive carrier (charges) causes various problems, such as a decrease in withstand voltage of the transistor element and formation of kink in the current-voltage relationship of the transistor element.